The invention relates to a filler head for a fuel tank of a motor vehicle, formed by a housing which is connected to the filler pipe which leads to the fuel tank, in which housing a neck which accommodates a fuel nozzle is provided and into which a recirculating line opens, wherein a venting line connects the uppermost region of the fuel tank to an activated carbon filter, and the recirculating line branches off from the venting line and extends to the filler head.
Environmental protection requires that fuel and fuel vapors must not enter the environment under any circumstances. Firstly, the fuel tank and all the lines which conduct fuel must be sealed, and it must also be possible to check this. Secondly, when refueling and during the operation of an activated carbon filter (ACF for short) fuel vapors must be intercepted or fed back into the tank or to the engine. In this context, the activated carbon filter must not come into contact with liquid fuel.
EP 1 600 317 A1 has disclosed an arrangement in which a venting line feeds the fuel vapors which are expelled during refueling to an ACF. A valve on the fuel tank ensures that in this context no liquid dropplets are carried along. In order to relieve ACF of loading, a recirculating line, which opens into the filler head and which makes use of the suction prevailing in the filler head or in the adjoining filler pipe during refueling in order to feed back into the tank the vapors which are expelled during refueling, branches off from the venting line. When the fuel tank has reached the highest level, the pump which feeds the fuel nozzle is switched off by a known mechanism.
However, if this mechanism does not respond or does not respond quickly enough, the level of liquid in the filler pipe rises to such an extent that liquid fuel passes into the recirculating line and from there on into the ACF. A throttle point in the recirculating line is proposed there as an admittedly inadequate preventive measure. However, liquid must be reliably prevented from being transferred into the ACF. In contrast, an advantage of the arrangement described in said document is that when the filler head is closed the seal of the fuel tank and of the filler pipe can be checked by applying a partial vacuum to the ACF. Checking the seal by means of an overpressure would be much more complicated.
WO 2004/026608 A1 discloses a venting arrangement which provides a spring-loaded needle float valve in the recirculating line in order to prevent liquid fuel from penetrating the recirculating line. The arrangement of the valve outside the filler head has the result that if the deactivation device fails the stream of liquid fills the filler head and can therefore also pass into the surroundings. The valve is illustrated only schematically. Nevertheless it is apparent that it is therefore not possible to check the seal by means of a partial vacuum applied to the ACF.
DE 38 23 973 A1 discloses a filler head into which not only a recirculating line but rather the entire venting line opens, and from where there is a direct connection to an ACF. However, this means that during refueling all the expelled vapors pass into the filler head. When the fuel nozzle is entirely opened, this is a considerable volume flow at high speed. The part of the vapors which is not carried back into the tank by the suction passes into the ACF through a valve arrangement which has a large number of deflection points and constrictions.
This valve arrangement is composed essentially of a float which surrounds the neck of the filler head which guides the fuel nozzle and which, in a floated-up position, closes off the outlet to the line which leads to the ACF. Apart from the design of this valve arrangement, which is unfavorable in terms of flow, complex and difficult to assemble, it is to be noted that it functions only when the filler pipe extends obliquely (but not in the case of an upright filler pipe).
However, said valve arrangement suffers from the fact that if the liquid level in the filler pipe rises it cannot close in good time because the difference in levels between the inlet into the valve chamber and the outlet to the ACF in this arrangement is at any rate much too small.
The object of the present invention is to provide a securing device which avoids the disadvantages described above and which prevents liquid fuel from penetrating into the ACF and flowing out into the surroundings under any circumstances, which securing device is lightweight and inexpensive to manufacture and mount and which ultimately permits checking of the seal by applying a partial vacuum to the ACF.